1. Field of the Invention
The present invention relates to a thin film magnetic head to be used in a hard disk device (hereinafter referred to as “HDD”), and more particularly to a thin film magnetic head coping with a magnetic recording medium having a high recording density, a manufacturing method thereof, a head gimbal assembly using the thin film magnetic head, and a HDD using the thin film magnetic head.
2. Description of Related Art
A magnetic head is mainly composed of an element for recording or reproducing information to or from a magnetic recording medium and the substrate on which the element is formed. The magnetic head is configured such that the element is opposed to a track portion on the surface of the magnetic recording medium and the magnetic head (or the substrate) itself automatically floats above the magnetic recording medium by a predetermined interval at the time of recording or reproducing of the information.
As the recording density of a HDD becomes higher, the performance of a thin film magnetic head is required to be higher. The requirement includes it that the tracks on a magnetic recording medium should be narrower. For achieving the improvement of the electromagnetic conversion efficiency of the magnetic head in response to the aforesaid requirement, it becomes important how to control the interval between the magnetic recording medium and the magnetic head. Now, the configuration of a magnetic head, a manufacturing method of the magnetic head having the configuration, and the like in related art are briefly described.
A schematic drawing of the bottom face of a magnetic head 1 viewed from the side of a magnetic disk is shown in FIG. 4. A macrograph of a cross section at a line 5-5 in FIG. 4, especially as to an element portion, is shown in FIG. 5. The magnetic head 1 is composed of an element portion 22 and a slider 20. The element portion 22 is formed at a tip portion of a nearly cuboid ceramic board such as alumina titanium carbide (ALTIC), and performs recording and reproducing of information to the magnetic disk. The slider 20 is made of a ceramic board.
The element portion 22 is formed on the ceramic board by means of a thin film forming technique, a thin film working technique and the like, all being used in, for example, a semiconductor manufacturing process. As being exemplified in FIG. 5, the element portion 22 is composed of a reproducing element portion 22a including a reproducing element and a recording element portion 22b including a recording element. The reproducing element portion is formed by the formation of the following layers on one end face of the ceramic board 101 in order and by the working of them. The layers are an insulating layer 102 made from, for example, alumina, a lower part shielding layer 103 of the reproducing element portion, which layer 103 is made from a magnetic material, a shield gap layer 104 made from an insulating material such as alumina or the like, a reproducing element 105 such as an MR element or the like and an electrode layer (not shown) connected with the reproducing element 105 electrically, and an upper part shielding gap layer 107 made from an insulating material such as alumina or the like.
The recording element portion is formed by the formation of the following layers on the upper part shielding gap layer 107 in order and by the working of them. The layers are a lower part magnetic pole layer 108 for the recording element, which layer 108 is made from a magnetic material and works also as an upper part shielding layer of the reproducing element portion; a recording gap layer 109 made from an insulating material such as alumina or the like; a thin film coil 112, which is made from copper or the like, being an electric conductor, and is separated by the insulating material; and an upper magnetic pole layer 116 made from a magnetic material. After the formation of the layers and the working or them, an overcoat layer 117 made from alumina or the like is formed, and then the element portion is completed.
After the formation of the element portion 22, the bottom face of the magnetic head 1, or the bottom face of the slider 20 (the surface 110a of the board 101 shown in FIG. 5), is further worked in order that the bottom face operates as a specific plane, or an air bearing surface (hereinafter referred to as “ABS”) to the magnetic disk. The specific plane has a nearly perpendicular positional relation to the end face of the board 101, on which the element portion is formed. The ABS concretely makes the magnetic head 1 operate such that the slider floats above the surface of the magnetic disk by a extremely slight amount of interval by means of an air flow produced by the rotation of the magnetic disk and the amount of the floating is fixed. In the example shown in the drawings, a recessed portion 21b is formed by the scraping of a flat surface by ion milling or the like, and the other portion where the scraping is not performed is formed as a projecting portion being a rail 21a. 
By the performance of the working described above, it becomes possible to float the magnetic head 1 above the surface of the magnetic disk at a predetermined height and to hold it. On the other hand, for the performance of recording and reproducing at a desired signal strength to the magnetic disk, it is needed to set an MR height designated by Mt in the drawing as to the reproducing element at a predetermined value, or to set a throat height designated by St or the like as to the recording element at a predetermined value. Generally, polishing working of the bottom face of the slider 20 is performed for the setting of the MR height or the like to the predetermined values.
Conventionally, the precision of the values of the MR height and the like is heightened by the heightening of the precision of working at the time of the polishing of the bottom face of the slider 20 (or the surface 101a of the board 101). Moreover, the precision of the flatness and the roughness of the rail 21a is heightened by the improvement of the precision of polishing conditions. The interval between the magnetic disk and the recording and reproducing element is controlled by the achievement of the heightening of the precision of such values, the optimization of the shape of the recessed portion 21b and the improvement of the precision of the working of the recessed portion.
As described above, the working for making the MR height and the like to be the predetermined values, the working for making the rail surface 21a flat, and the like after the formation of the element portion 22 are generally performed by means of polishing working using, for example, a diamond paste and a polishing plate composed of a soft metal or the like. However, the polishing speeds of the ceramic board 101, the thin film portions 102, 104, 107, 109 and 117 made from an insulating material such as alumina, the reproducing element portion 105 such as the MR element, and the magnetic thin films 103, 108 and 116 are different from each other. Consequently, steps are formed between the board surface 110a and the end faces of the aforesaid respective thin films.
Consequently, there is the possibility that a desired MR height and the like cannot be obtained, or the possibility that the interval between the surface of the magnetic disk and the element portion 22 cannot be kept to a predetermined value owing to the steps even if the desired MR height can be obtained. Moreover, there is the possibility that the steps cause a problem when the interval between the magnetic disk and the element becomes narrower than the present interval between them, though the steps are allowed in the present interval. Furthermore, it can be considered that the surface state of the board surface 110a and the surface state of the element portion 22 after polishing are different from each other besides the formation of the steps. The difference between the surface states has the possibility of exerting the influence to disturb an air flow on the ABS together with the steps.
Moreover, as described above, the formation of the recessed portion 21b to the board surface 111a is performed by the ion milling or the like. However, it is not easy to work the ALTIC board to be flat and uniform. Consequently, there is the case where very little irregularities, undulations or the like are produced on the bottom face of the recessed portion 21b. In the case where the irregularities or the like are produced, too, the influence of them is exerted as the interval between the magnetic disk and the element becomes narrower. Consequently, there is the possibility that the amount of the float of the magnetic head cannot stably be obtained.
It is also considerable to achieve the aforesaid flat making of the rail surface, the reduction of the steps and the working of the recessed portion 21b by using a corrosive liquid having selectivity. However, in the elements composed of a plurality of thin films laminated on one another, because the speed of corrosion has dependence to film qualities and the speed of corrosion of ALTIC itself changes in very little regions, it is actually difficult to obtain a smooth flat surface and the like by the corrosive liquid.
Moreover, as described above, the working of making the MR height and the like after the formation of the element portion 22 to be the predetermined values, the working for making the rail surface 21a to be flat, or the like is generally performed by means of the polishing working using, for example, a diamond paste and a polishing plate composed of a soft metal, or the like. The polishing working applies a shearing stress to a material to be an polishing object, and generates a partial ductile deformation or the shearing of the material on a surface to be polished. Thereby, the polishing working is done by performing the microscopic removal of the material. Consequently, it is considerable that a work-affected layer where crystallinity or the like in the magnetic layers has changed by the shearing stress or the like or a defect or the like induced by the sharing stress is generated in the material.
If such a work-affected layer or the like is produced in, for example, the MR element, there is the possibility that the electromagnetic characteristics thereof are also affected by the work-affected layer. It is considerable that these influences become remarkable in a magnetic head coping with high density recording in which the MR height is small.
Moreover, in the aforesaid polishing work, there is the case where a shearing stress is applied in a direction perpendicular to the plane on which each film is formed, for example, in a TMR element having the structure in which several atomic layers (equal to or less 1 nm) of an insulating thin film are put between magnetic films. In this case, it can happen, the case where the magnetic thin film on one side is elongated in the direction perpendicular to the film surface thereof owing to the ductility thereof and to be touched with the magnetic thin film on the other side and thereby the insulating state between them is broken.
Owing to the reasons described above, it is examined to use working methods such as the ion milling, reactive ion etching (RIE) and the like in addition to the conventional polishing working or as a post-process of the polishing working. However, there is the problem that these working methods have selectivity to working objects and the working speeds change according to the working objects. When the aforesaid element is exemplified, the polishing speeds to the following portions differ from one another: the ceramic board 101; the thin film portions 102, 104, 107, 109 and 117, each being made from an insulating material such as alumina or the like; the reproducing element portion 105 such as the MR element or the like; and the magnetic thin films 103, 108 and 116. Consequently, the steps are produced between the board surface 110a and the end faces of the aforesaid respective thin films as shown in FIG. 5.
Consequently, there is the possibility that a desired MR height and the like cannot be obtained, or the possibility that the interval between the surface of the magnetic disk and the element portion 22 cannot be kept to a predetermined value owing to the steps even if the desired MR height can be obtained. Moreover, there is the possibility that the steps cause a problem when the interval between the magnetic disk and the element becomes narrower than the present interval between them, though the steps are allowed in the present interval. Furthermore, it can be considered that the surface state of the board surface 110a and the surface state of the element portion 22 after polishing are different from each other besides the formation of the steps. The difference between the surface states has the possibility of exerting the influence to disturb an air flow on the ABS together with the steps.